its not quite your £50 but its closer starting at $290 called the Quantum
http://www.digitalartsonline.co.uk/news/hacking-maker/cheap-3d-printer-pops-out-designs-at-super-high-speed/
and remember all these Open HW versions are mostly capable of self replication, so you can share with others to spread the costs :)
for fun try printing one of these related to above post, cant find the open free link to the paper though...

actually if their using the Paper-Based 3D Printer Now Adds a Splash of Colour then heres some video you can compare samples, looks fine for producing a first draft "SylvieBarak" :)
http://www.gizmodo.co.uk/2012/11/paper-based-3d-printer-now-adds-a-splash-of-colour/
but a FORM 1 http://www.kickstarter.com/projects/formlabs/form-1-an-affordable-professional-3d-printer
would probably be better

I remember some of the first desktop laser printers being pretty expensive. There was one guy in our class that had one. The rest of us were printing near letter quality on dot-matrix.
So how long will it take for the 3D printer to make it down to the $50 level?

actually thinking about a little more they may get even better total throughput if they take the http://julialang.org/
"Julia is a high-level, high-performance dynamic programming language for technical computing, with syntax that is familiar to users of other technical computing environments. It provides a sophisticated compiler, distributed parallel execution, "
the http://www.youtube.com/watch?v=atAdpt5SZe8 "XMOS XMP-64 Development Board" for unlimited IO and control expansion and read up on these http://phys.org/news/2012-12-team-fractal-geometry-lighter.html algorithm papers then integrate it all in a small Open Hardware space

thats pretty cool, on a quick glance.
its a shame their thermal modeling software choice "code-aster" is so inefficient that it takes many cores to and time to perform its tasks
http://www.code-aster.org/V2/spip.php?article643 or you could use a bunch of these in a small cluster :)
Exynos 4412 ODROID-U2
http://www.hardkernel.com/renewal_2011/products/prdt_info.php?g_code=G135341370451
perhaps they will have another Code_Aster hackathon and re-factor it for AVX[2]/NEON SIMD sometime

The RepRap project has really brought the price of these printers down with (largely) self-printing. Kit prices go for as low as $500. I look forward to the metal version being presently developed called the MetalicaRap printer. They have a design goal of reducing the current cost of a 3d EBM printer by a factor of 100. Arcam's EBM printer presently costs about $500,000. See here, http://reprap.org/wiki/MetalicaRap